In German Patent Specification No. DE 2724060, there is disclosed a press suitable for the continuous production of thin chipboard and fibreboard. Such a press comprises a central, heated press drum which is mounted for rotation in suitable supports. An endless steel band passes around a major portion of the external surface of the press drum. The band also passes around a feed roller, a tensioning roller and a discharge roller. The chips or fibres are mixed with a bonding agent and are collected by the band. The material is subjected to a compression force between the drum and the strip and to a drawing force in the nip between the drum and the strip.
Modifications to such a press have been made with the aim of achieving higher outputs. In the main, the press length, that is to say, the length of the region in which the material is subjected to compression between the band and the drum, has been extended to achieve this. However, the complication arises that the time taken for the bonding agents to set remains unaltered. The increasing of the press length is usually effected, in the case of such rotary presses, by increasing the drum diameter. Presses of this type often have drums which have a diameter of 5 m, a bale length of approximately 3 m and a drum weight of approximately 110 t.
The press length, has in fact been extended by increasing the diameter of the central drum from 3 to 5 meters, so that a web having a thickness of, for example 3 mm can be compressed continuously to produce an output of up to approximately 40 m/min. The output rate is, in general, dependent upon the web thickness.
In order to operate economically, presses of this size and configuration must produce a high output to justify the extremely high capital investment required therefor.
When attempts were made to increase the output of such presses, however, it soon became apparent that the quality of the compressed chipboard or fibreboard web produced was unsatisfactory. Moreover, the service-life of the endless steel band became considerably shorter.